1. Field of the Invention
The present invention pertains to a process for improving the recovery of hydrocarbon fluids from a subterranean formation including micellar fluid--polymer fluid injection and creation of multiple fractures with propellant generated controlled pressure pulses.
2. Background
In recovering certain types of hydrocarbon fluids from subterranean formations, the injection of predetermined quantities or slugs of surfactants comprising micellar-type fluids may be carried out usually following injection of a conditioning slug of water or similar fluid into the oil reservoir. The surfactant recovers residual fluids such as heavy hydrocarbon oils by reducing interfacial tensions and by changing the phase behavior of the fluids. The injection process is usually carried out using one or more injection wells which are located in a predetermined pattern also including one or more production wells.
Stable displacement of the relatively viscous surfactant through the reservoir requires that the mobility of the surfactant slug should be less than the mobility of the preceding bank or slug of oil and water produced by the water flooding process. Moreover, the injection of the surfactant is usually followed by injection of a still more viscous and less mobile slug of polymer fluid which is designed to displace the slug of surfactant and recoverable oil toward the production wells.
In the early stages of the aforementioned type of flooding process, injection rates are relatively high because the viscosities of water and certain types of surfactants are relatively low. However, micellar type fluids, for example, have viscosities which can be on the order of ten to twenty times greater than the viscosity of a water-oil slug being displaced through a formation and, accordingly, the injectivity rate during the injection of the micellar fluid-type surfactant decreases dramatically as compared with the injection rate of a fluid such as water or other less viscous fluids. Since drive fluids such as polymer fluids must be more viscous than the micellar fluid type surfactant, in order to provide a stable displacement or sweep of the formation, the injectivity rate during polymer fluid injection also decreases with respect to the injection rate of the micellar fluid.
Accordingly, it is desirable to increase the injection rate of surfactants and similar oil mobilizing fluids as well as to increase the rate of injection of subsequent or preceding drive fluids which are injected into the same zone in order to reduce the amount of capital required to provide the injection process. In this regard, it is clear that the process of micellar fluid-polymer fluid type flooding, in particular, may be uneconomic if injection rates are low because of the large investment in chemicals and injection equipment which is required to be utilized over a relatively long period of time. Hence, methods for improving the fluid injectivity rate and the oil displacement rate toward the production wells are constantly being sought. It is an object of the present invention to improve the injection rate and the resultant recovery rate of a chemical flooding process, particularly of the micellar fluid--polymer fluid type process by providing multiple fractures in the formation region being injected to, in effect, increase the formation permeability and the rate of driving of the desired mineral values to be recovered toward one or more producing wells.